Experiments are proposed to compare the significance of histone-histone interactions in replicating and non-replicating nuclei and chromatin fractions from rat liver. The interruption of such interactions is postulated to be of significance in allowing the expression of non-replicative DNA polymerase activity as commonly assayed in nuclei and chromatin fractions in vitro. The proposed work is facilitated by 1) the availability of histone-binding polyanions some of which stimulate non-replicative in vitro DNA synthesis, and 2) the development in the applicant's laboratory of a simple procedure for the separation of the product of in vitro non-replicative DNA synthesis from the replicative product. This work should lead to improved understanding of 1) the requirements for histone interaction on the replication complex, and 2) the events leading to non-replicative DNA synthesis. It is expected that the overall results will contribute to our understanding of the control of mammalian cell division.